1. Field of the Invention
The present invention relates generally to electromagnetic modulating valves. More particularly, the present invention relates to valves utilizing permanent magnets and electromagnets to provide enhanced response times. Even more particularly, the present invention relates to a modulating electromagnetic valve which may be used in a vehicle shock absorber to vary the damping characteristics of the shock absorber.
2. Description of Related Areas of Art
U.S. Pat. No. 4,605,197 issued on Aug. 12, 1986 to Casey, et al for "Proportional And Latching Pressure Control Device" shows a proportional pressure control device which includes a motor having a housing and reciprocably movable armature which move between first and second limit positions. A poppet valve member is attached to one end of the armature adjacent a valve seat. Centering springs maintain the armature in a centered position with the poppet at a given distance from the valve seat. The fluid flow is controlled proportionally to the current induced in an electromagnetic coil element. Although several elements of this device are similar to the present invention, it is a proportional pressure control device, the length of armature stroke being proportional to the amount of electrical current being used. Dissimilarly, applicant's pulse-width modulated device always moves to each limit position in a cyclical fashion, the frequency of the movement determining the flow rate.
U.S. Pat. No. 4,794,890 issued to Richoson, Jr. on Jan. 3, 1989 for "Electromagnetic Valve Actuator" shows a bistable electromechanical transducer having a reciprocable armature which utilizes a permanent magnet latching arrangement. The permanent magnet latches the armature in each of its two limit positions and an electromagnet moves the armature between the two limit positions. The device further includes an arrangement for decelerating the armature and valve as the valve nears a limit position.
U.S. Pat. No. 4,127,835 issued to Knutson on Nov. 28, 1978 for "Electromechanical Force Motor" shows an electromechanical force motor which has an elongate magnetic casing housing a magnetic armature. The annular electromagnetic coil surrounds the armature and is axially positioned between a pair of permanent magnets having axially directed poles. Like the Casey, et al device, centering springs are used. Furthermore, unlike the present invention, permanent magnetic poles are axially directed as opposed to being radially directed.
U.S. Pat. No. 3,740,594 issued to Casey on June 19, 1973 for "Permanent-Electromagnetic Reciprocating Device" has a tubular, radially magnetized permanent magnet coaxially surrounding a long length armature. The permanent magnet and armature are closely spaced, having an electromagnetic coil in the gap therebetween.